A New Electrical Resistivity Tomography Scheme of Borehole-to-Surface-to-Cliff Detection and Imaging for Grotto Rock Structure

Grotto rock structure detection is precondition of the grotto protection and restoration. As a stable and non-destructive geophysical method, electrical resistivity tomography (ERT) is extensively used to detect the geological structure of the grottoes. However, the traditional ERT measurement scheme is challenging to satisfy the requirements of high accuracy and high resolution in the cliff region. Therefore, we propose a new borehole-to-surface-to-cliff ERT (BSC-ERT) scheme for grotto detection. The sensitivity patterns of five ERT schemes using three configurations (A-MN array, AB-MN array, and AM-BN array) are tested to show the detection capability of different configurations. Two numerical experiments show that the combination of borehole-to-surface ERT (BS-ERT) and surface-to-cliff ERT (SC-ERT) schemes using AM-BN array have better imaging effects and a more reasonable detection range, which is recommended to be implemented for future work. In addition, the numerical experiment also proves that the symmetric effect generated in the AM-BN array in BS-ERT scheme can be suppressed with the combination of the SC-ERT scheme.

Automated summary

Grotto rock structure detection is crucial for the protection and restoration of grottoes. Electrical resistivity tomography (ERT) is commonly used for this purpose. However, the traditional ERT measurements face challenges in terms of accuracy and resolution in cliff regions. To address this, a new BSC-ERT scheme is proposed, which combines borehole-to-surface ERT and surface-to-cliff ERT using the AM-BN array configuration. Numerical experiments show that this combination yields better imaging effects and a more reasonable detection range, making it recommended for future work. It is also demonstrated that the symmetric effect generated in the AM-BN array in the BS-ERT scheme can be suppressed with the combination of the SC-ERT scheme.